• Ram Prasad

      Articles written in Bulletin of Materials Science

    • Effect of heat treatment and composition on the superconductivity in Pb-Sr-R-Ca-Cu-O oxide system

      N C Soni Ram Prasad Kalyan Adhikary A Gulnar C V Tomy S K Malik

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      The effect of compositions, sintering temperatures and furnace atmospheres on the superconducting transition temperatures of several members of the series Pb2Sr2R1−xCaxCu3Oz(0.0⩽x⩽0.7, R=Y, Gd) has been studied. The effect of partial replacement of Pb, Ca and Y by In has also been studied. The shapes of the resistivity-temperature curves and the zero resistance temperatures are found to be extremely sensitive to the synthesis parameters employed. Superconductivity is not observed in samples treated in oxidizing atmosphere or heated at very high temperatures. Samples sintered in flowing nitrogen showed incomplete transition in resistivity starting at about 75 K and extending down to 15 K. A new and comparatively simple synthesis procedure involving treatment of the samples in vacuum has been employed to obtain nearly single-phase materials showing metallic behaviour. Using this procedure, samples of the above composition, but containing no Ca(i.e. Pb2Sr2RCu3Oz, R=Y and Dy), are also found to be superconducting with zero resistance up to 48 K.

    • 151Eu Mössbauer studies on Zn-doped EuBa2Cu3O7−y

      C V Tomy R Nagarajan S K Malik Ram Prasad N C Soni Kalyan Adhikary

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      151Eu Mössbauer studies have been performed on the compounds EuBa2(Cu1−xZnx)3O7−y withx=0·0, 0·025, 0·05, 0·075 and 0·1. The parent compound, EuBa2Cu3O7−y is superconducting with a transition temperature (Tc) of 88 K.Tc is depressed as Zn is substituted for Cu in this system and the compounds withx>0·05 do not show superconductivity down to 12 K.151Eu Mössbauer studies at 295 K show a single Mössbauer line in all the compounds (whether superconducting or not) with isomer shift value typical of Eu3 + ion. Further, the isomer shift values are nearly independent ofx and the temperatures down to 10 K. These observations imply that the Cu-O network responsible for superconductivity is very weakly coupled to the Eu sublattice.

    • Critical current density and magnetization studies on Bi(Pb)SrCaCuO

      P K Mishra Shailendra Kumar G Ravikumar P Chaddah B A Dasannacharya Ram Prasad N C Soni

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      HighTc phase (Tc ∼ 110 K) has been obtained in Bi-Sr-Ca-Cu-O system by partially substituting Bi by Pb. Magnetic hysteresis has been measured as a function of temperature. Critical current densities have been measured at 77 K both by transport and a.c. magnetization method in bulk samples for various concentrations of Pb. The results show that substitution of 15 at % Pb for Bi is most preferable for higher critical current density.

    • Crystal structure and resistivity studies on PrBa2 −xPrxCu3O7 −y oxide system

      S K Malik C V Tomy Ram Prasad N C Soni K Adhikari

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      The compound PrBa2Cu3O7 −y is not superconducting while most other RBa2Cu3O7 −y (R=rare earth) compounds exhibit superconductivity in the 90K range. The system PrBa2 −xPrxCu3O7 −x has been prepared to study the effect of excess Pr at the Ba site on the structure, resistivity and magnetic behaviour of this system. It is observed that single-phase compounds in the above series form forx=0·8—that is up to the composition Pr1·8Ba1·2Cu3O7 −y. While stoichiometric PrBa2Cu3O7 −y is orthorhombic, the compounds with excess Pr show tetragonal structure. Four-probe dc resistivity measurements show that all the single-phase compounds in the above series do not exhibit superconductivity and are semiconducting down to 12 K. Magnetic susceptibility measurements reveal deviation from Curie-Weiss behaviour starting at a characteristic temperature, which is taken to be the ordering temperature (TN) of the Pr moments. BothTN and overall resistivity decrease with increasingx and may have a common origin.

    • Plasma sprayed hydroxy apatite coatings

      D S Patil K P Sreekumar N Venkataramani R K Iyer Ram Prasad R S Koppikar K R Munim

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      This paper describes the method of producing plasma sprayed coatings of hydroxy apatite (HA) on metallic substrates of Ti-6Al-4V. Hydroxy apatite is a material which has similar composition to that of the mineral phase of the human bone. Poor mechanical properties however inhibits its use in the load bearing applications. The powders prepared in our laboratory are sprayed using a plasma spray torch operating in ambient. The deposited coatings are charaterized by X-ray diffraction and found to retain HA in the coatings as per requirements.

    • Effect of calcium substitution on superconductivity and hole concentration in La1·5Ba1·5Cu3Oz

      Nikesh A Shah D G Kuberkar B T Savalia M R Gonal Ram Prasad R G Kulkarni

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      The superconducting properties of single phase La1·5−xCax+yBa1·5−yCu3Oz, 0·0≤x≤0·60 (LC) and 0·0≤y≤0·70 (CB), compounds with tetragonal triple-perovskite structure are studied, using X-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La1·5−xCaxBa1·5Cu3Oz (LC) samples, 0·15≤x≤0·60, are superconducting withTcR=0 between 40 and 74 K. With the increase inx, the oxygen content, hole concentration in the CuO2 layers as well as theTc increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa0·5+yBa1·5−yCu3Oz (CB) compounds increase with the increase iny, theTcR=0 remains nearly constant around 74 K fory=0·0−0·70. A correlation exists between theTc and the hole concentration for LC and CB compounds.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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